1. Field of the Invention
The present invention relates to an internal combustion engine control apparatus provided with a function of correcting the ignition timing so as to suppress a knock from occurring, when based on a vibration produced in the internal combustion engine, it is determined that a knock has occurred; in particular, the present invention relates to an internal combustion engine control apparatus that prevents erroneous determination of a knock, while expanding the operation range of the knock suppression function at a time immediately after the inner-cylinder state of an internal combustion engine has changed from a non-combustion state to a combustion state.
2. Description of the Related Art
To date, there has been adopted an internal combustion engine control apparatus provided with a function of suppressing a knock from occurring by detecting with a knock sensor an inner-cylinder vibration produced when the internal combustion engine abnormally combusts and shifting the ignition timing toward the retarding side (delaying the ignition timing).
In an internal combustion engine control apparatus provided with such a knock suppression function, for example, a vibration of an internal combustion engine detected by a knock sensor is processed through a band-pass filter or the like so that only vibration components of specific frequencies are extracted; then, the value of a maximum level, in a predetermined crank angle range, of the vibration components of specific frequencies is extracted as a characteristic value of the vibration level in the present combustion cycle.
As the specific frequencies, frequencies (generally, frequencies of 5 through 15 kHz) are preliminarily selected with which the level of a vibration caused by the occurrence of a knock can be detected with high sensitivity. The crank angle range (generally, from the compression top dead center to approximately 60 [deg] after the compression top dead center), in which the level of a vibration caused by the occurrence of a knock can be detected with high sensitivity, is also preliminarily selected; in general, the crank angle range is referred to as a knock detection range.
After characteristic values for characterizing vibration levels are extracted, a background level (referred to as a BGL, hereinafter) is calculated by averaging the characteristic values through a filtering operation; the standard deviation of the characteristic values is calculated through a filtering operation based on the characteristic values and the BGL; then, a knock determination threshold value for determining of the occurrence of a knock is calculated based on the BGL and the standard deviation.
After the knock determination threshold value is calculated, it is determined whether or not a knock has been produced, by comparing the characteristic value with the knock determination threshold value. In the case where the characteristic value is the same as or smaller than the knock determination threshold value, it is determined that no knock has been produced; then, the knock intensity indicating the intensity of a vibration caused by a knock is set to “0”. In contrast, in the case where the characteristic value exceeds the knock determination threshold value, it is determined that a knock has been produced; then, the knock intensity is calculated based on the characteristic value, the BGL, and the knock determination threshold value. After the knock intensity is calculated, a knock retarding amount corresponding to the knock intensity is calculated; then, the ignition timing is shifter by the retarding amount toward the retarding side.
When through a series of foregoing processing items, it is determined that a knock has been produced, based on the vibration of the internal combustion engine detected by the knock sensor, the ignition timing is shifted toward the retarding side in accordance with the intensity of the vibration caused by the knock, so that the occurrence of a knock is suppressed.
Meanwhile, it is known that the level of a vibration that can be detected by a knock sensor largely varies depending on the operation status of the internal combustion engine. For example, when an internal combustion engine in the stop mode is started, supply of a fuel into the internal combustion engine, which has been started to rotate by a starter motor, is started, and a compressed fuel-air mixture is ignited; combustion occurs inside the cylinder; transition from the non-combustion state to the combustion state is made; then, the internal combustion engine comes into the starting mode. In this starting mode, the internal combustion engine is in a transient mode where the rotation speed thereof transiently changes before it comes into a stabilized operation status; therefore, the level of a vibration that is detected by the knock sensor largely changes.
Accordingly, in the case where when the internal combustion engine is in the starting mode, the foregoing BGL and standard deviation are calculated by utilizing the filter coefficient, as it is, that is set to an appropriate value based on the assumption that the internal combustion engine is in a steady operation status, the filtering effect becomes extremely high, whereby the tracking capability for the behavior of the largely changing characteristic value is deteriorated; as a result, the knock determination threshold value becomes inappropriate, whereby there is posed a problem that knock determination is erroneously implemented.
Accordingly, in Patent Document 1 (Japanese Patent Application Laid-Open No. 2006-183662), there has been proposed a technology in which when an internal combustion engine is being started, knock determination is prohibited until a time required for the BGL calculated through a filtering operation to catch up with a right value elapses. This conventional technology prevents the erroneous determination caused by a tracking delay in the filtering operation at a time when the internal combustion engine is started.
Moreover, in Patent Document 2 (Japanese Patent Application Laid-Open No. H4-140454), there has been proposed a technology in which based on the changing level of the rotation speed of an internal combustion engine, it is determined whether or not the internal combustion engine has come into a transient operation status, and in the case where it is determined that the internal combustion engine has come into a transient operation status, the filter coefficient for calculating the BGL is shifted to the side where the filtering effect is weakened. This conventional technology prevents erroneous knock determination caused by a tracking delay in the filtering operation at a time when the internal combustion engine is in a transient operation status.